Multi-user, Multi-Input Multi-Output (Mu-MIMO) radio communication systems, many of which have historically been deployed in cellular communication systems, have been proposed in which a base station MIMO antenna is used to communicate, for example in the downlink direction, with several separate radio terminals, such as mobile devices, typically terminal devices such as User Equipment (UE) nodes. Massive MIMO systems have also been proposed in which radio access points, such as but not limited to cellular base stations, are equipped with a large number of antennas, for example in which the number of antennas at the radio access point is greater than the number of terminals that are communicatively coupled to the radio access point.
In a conventional multi-access wireless communications network, communications between a user terminal and a base station within a sector is performed by orthogonalizing the channel using schemes such as orthogonal coding, frequency separation, and/or time separation. Because there are a limited number of orthogonal resources available, this approach is inherently limited with respect to the overall number of UEs, that can be served within a sector.
Existing communication schemes incorporating massive MIMO typically rely on use of interference cancellation precoding schemes such as Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) algorithms. These approaches to massive MIMO attempt to suppress multi-user interference (MUI) through interference cancelation. However, these methods are limited to serving UEs that have relatively long coherence times and low channel correlations. Furthermore, these methods produce transmit beams which can vary significantly depending upon the geographic distribution of terminals and therefore do not guarantee port orthogonality between channels, for example such that the coupling or cross-talk between ports of different channels cannot be reliably maintained near zero. This can lead to significant loss of capacity due to loss in system performance as a result of channel coupling.
Therefore there is a need for a method and system for Spatial Multiplexing Mu-MIMO radio communications, that obviates or mitigates one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.